Door phone controllers have been used to allow host telephone equipment to function as both an ordinary telephone for placing outside or central of f ice line telephone calls and to operate a security door, such as an apartment building entrance door, by providing a paging/intercom system with a speaker located by the security door. The door phone controller allows the person inside the building to open the door via a door-unlock push-button or through dual tone multi-frequency (DTMF) signalling via the host telephone's keypad. Either of these actions, i.e. pressing the door-unlock push-button or dialing the DTMF code, closes metallic contacts which then activate the customer-provided electric door release or latch.
Known systems provide a latch driving device, the primary purpose of which is to activate an electric door strike plate when the proper DTMF code is detected. The electric door strike plate remains active for an adjustable period of time, for example 1-15 seconds, thus allowing the door to be opened. A reset switch, e.g. a "Reed" relay, is provided to de-activate the latch after the door is opened, regardless of the adjustable activation setting. However, this latch driving device does not provide the user with any indication as to whether the door has been left ajar.
Another known system which is computer based provides a door ajar signal to the user by either displaying which door is ajar on a cathode ray tube (CRT) or by activating metallic contacts which in turn activate a customer-provided alerting device. However, this door ajar system provides no variability with respect to its operation and thus is not adaptable to the individual user's needs.
There is therefore needed a system and method for alerting a user through the host telephone system when an entrance door has been left ajar or, has ever been opened. Such a system should be adaptable to the individual needs of the user and be simple to operate.